You seem to imply that we can not change the energy balance of our planet by any means that generates power, yet you concede that the byproduct that is generated by the fossil fuel power generation will add to the global heat energy.

You say that: “Because of greenhouse gases, the earth’s ability to radiate excess heat into space is impaired”
I do not fully comprehend the ability of the greenhouse gasses to retain the energy that they receive.
If I understand it correctly, in a actual greenhouse the radiative heating that comes from the sun increases the temperature of the material, including the air, then the glass or plastic covering prevents the convection effect from cooling the air that is trapped inside, that way the air in the confined area remains warm for a long period of time. In other words, the conductive and radiative heat loss is minimal compared to the convective heat loss.
The Earth does not have a glass or plastic covering to prevent convective heat loss.
How does the greenhouse gas prevent convection heat loss or radiative heat loss for that matter?

Going back to the atomic reactions,
From: http://en.wikipedia.org/wiki/Uranium-235

“The fission of one atom of U-235 generates 202.5 MeV = 3.24 × 10−11 J, which translates to 19.54 TJ/mol, or 83.14 TJ/kg.

Now if we knew how many fissioning U-235 atoms there are in the 65,000 tonnes of waste material that is stored in the US, we could find out how much energy is released from that waste by those atoms, then we also could find out how much waste there is in the rest of the world and how much is in the operating reactors,-- I think you get the idea, I'm sure that the number of TJ/kg will be very large, even if it is small compared to the sun's energy, it is an ADDITION to the energy that comes to us from the sun.
I Suppose that burning a single candle for thousand years will give the same amount of energy as burning a thousand candles for a single year. The thing is that a thousand candles that would surround me now would keep me warmer that the single candle.
Even though the generated 374,411 MW(e) + may keep us warm for a while, it may also be the proverbial straw that breaks the camels back.
Conclusion in four words: Heating: Expansion: Cooling: End.